The present invention has been developed for its particular applicability to the processing of semiconductor wafers. Semiconductor wafers must be processed in an extremely clean environment and process liquids and coatings must be very accurately applied.
Processing fluids and coatings include, for example, liquid resist materials which are subsequently patterned to create electrical circuit features, and other coatings such as anti-reflective coatings. Resist materials typically include organic solvents while other coatings may be soluble organically or in water. One common water soluble top anti-reflective coating is known as Aquatar.TM. which is available from AZ Photoresist Products, a division of Hoechst Celanese Corporation of Somerville, N.J.
Semiconductor wafers are typically coated within a coating apparatus known as a spinner or spin-coater. A spin-coat process is performed within a process chamber, wherein a rotatable chuck is driven with a semiconductor wafer supported thereon while process fluid is deposited onto the surface of the wafer. The process chamber is also exhausted, preferably by a negative pressure system, through an exhaust system. During the spin-coat process, process fluid is ejected from the wafer surface onto a cup assembly, typically provided within the process chamber, and airborne process fluid and particles are exhausted through the exhaust system. This process fluid may subsequently deposit and dry on the surfaces of the cup assembly and the exhaust system. This dried process fluid can provide potential contaminants within the coating process.
It is desirable to maintain the spin-coat process chamber as clean as possible. In this regard, developments have been made for periodically cleaning the internal surfaces of the process chamber. For example, in U.S. Pat. No. 5,312,487 to Akimoto et al, several methods and devices are disclosed for applying cleaning or rinsing fluid to the internal surfaces of the container making up the process chamber. The purpose is to reduce the potential of contaminants being introduced from the process chamber onto a subsequently coated wafer. The coating materials as well as the washing liquids are exhausted through a conventional exhaust system and/or its drain.
Other cleaning systems have also been developed for use within a process chamber for the purpose of cleaning the back side of a semiconductor wafer after it is coated. Specifically, cleaning fluid is directed against the wafer back side with a controlled airflow over the wafer and into the exhaust system for cleaning the wafer back side and exhausting the removed particles and cleaning liquid. An example of this type of apparatus is disclosed in U.S. Pat. No. 5,529,626 to Stewart.
In these prior art systems, however, the coating fluids and cleaning liquids entrained within the airflow are carried into the exhaust system. An exhaust system will typically include exhaust manifolds and exhaust control mechanisms for controlling airflow. As the process fluid becomes airborne and is carried into the exhaust system, an incremental buildup of the process fluid on the exhaust system parts occurs. This incremental buildup can affect exhaust control performance by disturbing the requisite airflow normally controlled by a control valve and can eventually result in a restricting of the airflow passage altogether.
Exhaust systems also typically include a butterfly type valve as an airflow control valve for setting the requisite airflow desired for a particular coating application. Flat screens are also typically provided within the exhaust system for catching larger particles within the exhaust system, such as broken wafer pieces in the event of a wafer mishap in the spinner, to prevent damage to the exhaust system. These butterfly type valves and screens are also subject to the incremental buildup of process material carried within the exhaust.
Thus, exhaust systems typically require periodic disassembly and cleaning. However, periodic disassembly and cleaning is disadvantageous not only due to the downtime of the coating apparatus, but also in that disassembly compromises the system integrity by introducing the potential for particles to be introduced into the system.
Cleaning processes, such as described in the aforementioned U.S. Pat. Nos. 5,312,487 and 5,529,626, are beneficial to the exhaust system in the sense that cleaning or rinsing fluids are also carried into the exhaust system on a periodic basis. However, the airborne fluids within the exhaust during such cleaning processes also include the airborne coating materials. Thus, any benefit is relatively minimal. Another way to clean the exhaust system is to simply periodically dump solvents or cleaning fluids within the cup of the spinner assembly so that the fluid flows through the exhaust system for cleaning it. Such a procedure can be performed on a periodic basis also to prevent buildup of coating materials within the exhaust system. However, such a procedure still requires maintenance time and for an operator to manually dump the cleaning fluids within the apparatus. Moreover, a relatively large amount of cleaning fluid is required in order to ensure that all contaminated surfaces of the exhaust system are adequately cleaned. Then, all the cleaning fluid must be handled throughout the exhaust system.
Alternatively, obstructions to the flow of the exhaust air including airborne coating material can be eliminated. Items such as butterfly type control valves and screens can obstruct the airflow, particularly after a buildup of coating material thereon. These items may simply be removed from the exhaust stream. However, the clear disadvantage is the loss of control of the airflow and/or the safeguard features provided thereby. Moreover, at some point, the piping may still require cleaning.